Typically, articles having smooth, mold-imprinted surfaces are used in trim components for interior designs, e.g. in cars or airplanes, and external car parts. The Automotive industry imposes stringent requirements for finished parts. Low total carbon emission, low fogging and low odor with good scratch resistance are typical requirements for interior trim such as instrument panel, door panels and quarter panel trim that are typically injection molded. The exterior parts, including bumper assemblies and structural modules such as front end module carrier, typically require high performance filled compounds. Exterior trims like side protection trims, cowl grills, wheel arch liners and covering parts like rocker panels, body side mouldings or fender liners demand specific properties in combination with good surface appearance.
U.S. Pat. No. 6,441,094 discloses impact resistant polyolefin compositions comprising two polymer fractions with different Melt flow rate values (bimodal matrix) and a rubbery phase formed by an elastomeric copolymer of ethylene. The polyolefin composition in U.S. Pat. No. 6,441,094 present a unique Balance of processability and mechanical and optical properties and they are particularly suitable for injection molding parts.
Materials used for exterior and interior trims need to deliver flexibility combining properties like narrow gap tolerances, superior scratch resistance and good paint adhesion and processability.
Due to their free-flowing characteristics, different blends filled with talcum have been used in such applications hitherto. The potential of talcum-reinforced blends is limited for molding of rigid finished articles, such as car dashboards, due to their inherent low flexural stiffness. Recently low density materials keeping high mechanical performance are desired to match increasing demand for lightweight car-parts to increase fuel efficiency, without deteriorating safety, and performance. Talc filled compositions are known to provide increased stiffness performance with the increase of the filler amount at the expense of an increase of weight. Reducing talc brings normally to a reduction of stiffness that can be compensated increasing stiffness of the polymeric components, nonetheless this is normally at the expense of shrinkage and thus impacting negatively on the narrow gap tolerance in molds.
It would be desirable to avoid the disadvantages of the prior art to devise a new low density light weight composite material for molded articles retaining the advantages of the prior art blends, notably their excellent free-flowing properties and shrinkage and impact/stiffness balance.
The compositions of the invention are suitable for conventional molds with comparable “gap tolerance” and “tool shrinkage” as for higher density compositions known in the state of the art.
Thus, the inventive composition is a valuable drop-in solution in the automotive field by using existing moulds with economic advantage and security of supply.